Fig. 1

a Schematic of the Fe-Co₄N@N–C nanosheet grown on CC for application in the bifunctional oxygen reaction [56]. b Schematic depicting the synthetic process for Co@NCNTAs [85]. c Schematic of the synthetic process for CoFe@NCNT/CFC [98]. d Schematic of the preparation of MnO_x-CC-400 [2]. e Proposed phase transition of manganese oxide on CC via a thermal treatment [2]. f Schematic of the ZIF-L-D-Co₃O₄/CC formation process [24]. g Schematic of a 1 nm-CoO_x layer on the metallic substrate of Co/N-RGO [23]. h Schematic of the fabrication processes for the squeezable and rechargeable all-solid-state ZABs [27]